If you don't know your positive + from your negative - then I suggest you take it to a professional.
If you think you know how to do it yourself then the process is quite simple:
1: Remove your old stereo. You may need special keys to do this.
2: Disconnect the wiring at the rear of the unit. This should be as simple as unplugging the plugs.
3: Pickup a simillar plug from your local Halfords or car accessory shop and just follow the the same routing for the color coordinated wires.
Its that simple.
Adeboy
December 2004